Extracorporeal Membrane Oxygenation Blood Flow and Blood Recirculation Compromise Thermodilution-Based Measurements of Cardiac Output

The contribution of veno-venous (VV) extracorporeal membrane oxygenation (ECMO) to systemic oxygen delivery is determined by the ratio of total extracorporeal blood flow ([Formula: see text]) to cardiac output ([Formula: see text]). Thermodilution-based measurements of [Formula: see text] may be compromised by blood recirculating through the ECMO (recirculation fraction; Rf). We measured the effects of [Formula: see text] and Rf on classic thermodilution-based measurements of [Formula: see text] in six anesthetized pigs. An ultrasound flow probe measured total aortic blood flow ([Formula: see text]) at the aortic root. Rf was quantified with the ultrasound dilution technique. [Formula: see text] was set to 0–125% of [Formula: see text] and [Formula: see text] was measured using a pulmonary artery catheter (PAC) in healthy and lung injured animals. PAC overestimated [Formula: see text] ([Formula: see text]) at all [Formula: see text] settings compared to [Formula: see text]. The mean bias between both methods was 2.1 L/min in healthy animals and 2.7 L/min after lung injury. The difference between [Formula: see text] and [Formula: see text] increased with an [Formula: see text] of 75–125%/ [Formula: see text] compared to Q(EC) <50%/ [Formula: see text]. Overestimation of [Formula: see text] was highest when [Formula: see text] resulted in a high Rf. Thus, thermodilution-based measurements can overestimate cardiac output during VV ECMO. The degree of overestimation of [Formula: see text] depends on the [Formula: see text] (EC)/ [Formula: see text] ratio and the recirculation fraction.